The present invention relates to a resin material for an electrical insulating material characterized in comprising an ethylene xcex1-olefin copolymer possessing a superior processability and thermal resistance, in addition to an excellent mechanical strength and electrical insulating properties; an electrical insulating material and electric wire and cable using the same. Specifically, the present invention relates to a resin material for an electrical insulating material possessing superior electrical insulating properties, such as volume resistivity, space charge characteristics, dielectric breakdown strength, and the like; a resin material for an electrical insulating material in which even after cross-linking, degradation of electrical insulating properties, e.g., volume resistivity, space charge characteristics, dielectric breakdown strength, and the like does not occur; and an electrical insulating material formed from the aforementioned resin material and cross-linked product, and electric wire and cable possessing an insulating layer using the same. This application is based on a patent application filed in Japan (Japanese Patent Application No. Hei 10-262105), the contents of which are incorporated herein by reference.
Conventionally, electrical insulating materials for electric wire and cables fundamentally require a high volume resistivity, and a high dielectric breakdown voltage, in addition to a low dielectric constant and dielectric dissipation factor, for which a polyethylene or the like is generally used. In addition, as an electric power cable for use in mass transmission, such as a high-tension power cable and the like, a cable which uses an insulating material to which oil has been filled (hereinafter referred to as xe2x80x9cOF cablexe2x80x9d) is routinely employed. However, this OF cable, despite possessing excellent electrical insulating properties, is disadvantageous in that oil often leaks out, which in turn necessitates a means for continuously supplying oil. In recent years, a cross-linked polyethylene has been used which possesses an increased thermal resistance and mechanical strength, and is obtained by means of cross-linking the polyolefin of a polyethylene or the like.
One of the problems associated with this high-tension power cable, which uses a cross-linked polyethylene in its electrical insulating material, relates to the power loss that occurs during high-tension transmission. Hence, the reduction of this aforementioned power loss is highly desirable. It is possible to reduce this power loss by means of increasing the electrical insulating performance of the electrical insulating material, in particular by increasing the volume resistivity.
However, even by simply increasing the volume resistivity at either room temperature or constant temperature, this leads to other problems as described below. For example, in a power cable, the electrical insulating material around the inner conductor will reach 90xc2x0 C. from the Joule heat of the electric current, however the electrical insulating material around the outer conductor remains at atmospheric temperature. In the case of an electrical insulating material employing a conventional polyethylene in which extreme reductions in the volume resistivity accompany temperature increase, an electrical field is concentrated around the interface of the outer conductor and insulating member, which reduces the dielectric breakdown strength. This phenomenon, in particular, creates large problems with regard to dc electric power cables. Accordingly, it is highly desirable to decrease the temperature dependence of the volume resistivity of the electrical insulating material.
With regard to a method for improving the temperature dependence of the volume resistivity of the electrical insulating material, a method is proposed in which maleic anhydride is grafted to a low pressure process polyethylene (e.g., Japanese Patent Application, First Publication No. Hei 2-10610 and the like). However, as an electrical insulating material, the electric power cables using this low pressure process polyethylene shows an inferior flexibility when compared with convention electric power cables.
In this manner, as an electrical insulating material, electric power cables using a low density polyethylene to which maleic anhydride has been grafted are proposed in Japanese Patent Application, First Publication No. Sho 63-150810, Japanese Patent Application, First Publication No. Sho 63-150811 and Japanese Patent Application, First Publication No. Hei 2-119012. However, the electrical insulating materials used in these electric power cables are disadvantageous in that the volume resistivity is reduced at high temperature.
In addition, in Japanese Patent Application, First Publication No. Hei 5-266723, an electrical insulating material is obtained by means of blending 100 parts by weight of a low density polyethylene, possessing a density of 0.92 g/cm3, and 0.5 to 20 parts by weight of a linear low density polyethylene, possessing a density of 0.91 to 0.94 g/cm3. However, the improvement of the temperature dependence of the volume resistivity provided by means of this electrical insulating material is inadequate, since this electrical insulating material does not sufficiently improve the volume resistivity around the inner conductor.
In addition, a polyolefin such as polyethylene or the like, which is used as an electrical insulating material for electric wires and cables, may be employed after undergoing cross-linking in order to increase properties such as the thermal resistance and mechanical strength.
As methods for cross-linking a polyolefin such as polyethylene, an electron beam cross-linking method and a chemical cross-linking method, which uses peroxides, are known. However, the electron beam cross-linking method requires large scale equipment, and possesses the disadvantage of high cost. In addition, the chemical cross-linking method, although economical, results in problems due to the existence of an unreacted cross-linking agent, as this residue causes reduction of the volume resistivity, degradation of the space-charge characteristics, and generation of water-treeing.
As a method for improving the electrical insulating properties, e.g., volume resistivity, space charge characteristics, water-treeing resistance, etc., a method in which a maleic anhydride-modified polyolefin is added to polyethylene in order to introduce hydrophilic group is proposed in Japanese Patent Application, Second Publication No. Hei 5-15007. Furthermore, a trial is being conducted in an attempt to improve the electrical insulating properties by means of introducing a double bond into the polyolefin prior to cross-linking, and reducing the addition amount of the cross-linking agent (Japanese Patent Application, First Publication No. Hei 4-11646). However, all of the aforementioned fail to produce both adequate electrical insulating properties, e.g., volume resistivity and the like, and thermal resistance.
On the other hand, technology for improving the electrical insulating properties of electrical insulating material such as the volume resistivity, dielectric breakdown strength and the like is being proposed in which a carbonic acid compound and/or aromatic compound is mixed into a polyolefin. For example, various technologies are being proposed for improving the impulse breakdown strength by means of grafting a styrene to a polyolefin (Japanese Patent Application, First Publication No. Hei. 2-165506); improving the impulse breakdown strength by means of blending a polystyrene into polyethylene (Japanese Patent Application, First Publication No. Sho. 63-301427); improving the electrical insulating properties such as volume resistivity and the like means of blending a maleic acid-modified polyolefin into a polyethylene (Japanese Patent Application, First Publication No. Sho. 62-1000909); improving the dielectric breakdown characteristics by means of blending an aromatic carboxylic acid into a polyolefin (Japanese Patent Application, First Publication No. Sho. 60-23904); and the like.
However, all of the aforementioned technologies are not able to achieve sufficient improvement of both the volume resistivity and dielectric breakdown strength. In addition, the electrical insulating properties even after cross-linking are inadequate.
On the other hand, Japanese Patent Application, First Publication No. Hei 9-17235 discloses electrical insulating material comprising a high mechanical strength and low electrical activation energy by means of employing a specific ethylene copolymer of a narrow composition distribution.
However, the composition distribution of the aforementioned ethylene copolymer is extremely narrow, while the change in viscosity and strength with respect to temperature is extreme, which in turn leads to narrowing of the appropriate range of conditions such as the temperature at the time of polymer processing, extrusion conditions, and the like, and results in poor processability.
In addition, an electrical insulating material employing an ethylene polymer manufactured by means of using a metallocene catalyst, and electric wire and cable using the same are disclosed in Japanese Patent Application, First Publication No. Hei 6-509905, Japanese Patent Application, First Publication No. Hei 8-111121, and Japanese Patent Application, First Publication No. Hei 8-222026. However, although these disclosures achieve an improvement in the treeing resistance, the appropriate range of conditions such as the temperature at the time of polymer processing, extrusion conditions, and the like are narrow, which in turn results in poor processability.
As a means for improving the processability of the ethylene polymer manufactured by means of using a metallocene catalyst, methods are known in which components of differing molecular weights are blended together, or the ethylene polymer is polymerized in multiple stages. However, even when using these types of means for improving the processability, it is still difficult to always achieve a sufficient improvement in the processability of the ethylene polymer manufactured by means of using a metallocene catalyst.
Furthermore, a method for blending an ethylene polymer manufactured by means of using a metallocene catalyst, and ethylene polymer of different molecular weight manufactured by means of using a Ziegler catalyst or a Phillips catalyst, are disclosed in, for example, Japanese Patent Application, First Publication No. Hei 9-505090. However, the dispersability of the aforementioned is insufficient, resulting in disadvantages such as melt fractures, and reduction of the mechanical strength.
In order to solve the aforementioned problems, Japanese Patent Application, First Publication No. Hei 9-302160 discloses a resin composition for an electrical insulating material comprising a resin component of an ethylene homopolymer or an ethylene copolymer satisfying specific parameters, such as a density of 0.86 to 0.96 g/cm3, MFR of 0.01 to 200 g/10 minutes, molecular weight distribution (Mw/Mn) of 1.5 to 5.0, a composition distribution parameter of no greater than 2.00, and an electrical activation energy of no greater than 0.4 eV, which contains a monomer unit selected from among a carbonyl or carbonyl derivative group-containing monomer, hydroxyl group-containing monomer, nitro group-containing monomer, nitrile group-containing monomer, aromatic ring-containing monomer and a compound or monomer containing two or more ethylenic linkages. However, a resin composition for an electrical insulating material, which further improves properties such as thermal resistance and the like, is required.
The present invention provides a resin material for an electrical insulating material possessing a superior processability and thermal resistance, in addition to superior electrical insulating properties, such as volume resistivity, space charge characteristics, dielectric breakdown strength, water-treeing resistance, and the like, in which a reduction in the mechanical strength does not occur; or a resin material for an electrical insulating material which is rich in cross-linkability, and even after cross-linking, exhibits superior volume resistivity, space-charge characteristics, dielectric breakdown strength, water-treeing resistance and the like; and an electrical insulating material formed from the aforementioned resin material and/or cross-linked product, and electric wire and cable possessing an insulating layer using the same.
The resin material for an electrical insulating material according to the present invention is characterized in that the resin component thereof comprises an ethylene xcex1-olefin copolymer (A), obtained by means of copolymerizing ethylene and C4-12 xcex1-olefin, said ethylene xcex1-olefin copolymer (A) satisfying specific parameters (i) to (v):
(i) a density of 0.92 to 0.96 g/cm3,
(ii) a melt flow rate (MFR) of 0.01 to 200 g/10 minutes,
(iii) a molecular weight distribution (Mw/Mn) of 1.5 to 5.0,
(iv) possessing only one peak in terms of the number of peaks observed in an elution temperature-eluted amount curve as measured by the continuous temperature raising elution fractionation (TREF) method, and from the integrated elution curve obtained by said elution temperature-eluted amount curve, the difference T75xe2x88x92T25 in the temperature and said density d respectively follow the relationships shown by formula a and formula b, wherein T25 is the temperature where 25% of the total elution is obtained, and T75 is the temperature where 75% of the total elution is obtained; and (v) possessing one or two melting point peaks, and among these the highest melting point Tm1 and said density d follow the relationship described by formula c;
wherein said resin component contains a unit (B) derived from at least one type of monomer selected from among a carbonyl or carbonyl derivative group-containing monomer (M1), a hydroxyl group-containing monomer (M2), a nitro group-containing monomer (M3), a nitrile group-containing monomer (M4), an aromatic ring-containing monomer (M5) and a compound or monomer containing two or more ethylenic linkages (M6); and when said unit (B) is derived from at least one type of monomer selected from M1 to M5, the concentration of said unit (B) ranges from 5xc3x9710xe2x88x927 to 5xc3x9710xe2x88x923 mol per one gram of said resin component, and when said unit (B) is derived from M6, the number of ethylenic linkages per 1000 carbon atoms of said resin component is at least 0.8.
if d less than 0.950 g/cm3, thenxe2x80x83xe2x80x83(Formula a)
T75xe2x88x92T25xe2x89xa7xe2x88x92300xc3x97d+285
if dxe2x89xa70.950 g/cm3, then
T75xe2x88x92T25xe2x89xa70
xe2x80x83T75xe2x88x92T25 less than xe2x88x92670xc3x97d+644xe2x80x83xe2x80x83(Formula b)
Tm1xe2x89xa7150dxe2x88x9217xe2x80x83xe2x80x83(Formula c)
This resin material for an electrical insulating materials displays superior processability and thermal resistance, in addition to superior electrical insulating properties, such as volume resistivity, space charge characteristics, dielectric breakdown strength, water-treeing resistance, and the like, in which a reduction in the mechanical strength does not occur. In addition, the resin material for an electrical insulating is rich in cross-linkability, and even after cross-linking, exhibits superior volume resistivity, space charge characteristics, dielectric breakdown strength, water-treeing resistance and the like.
In addition, the aforementioned ethylene xcex1-olefin copolymer (A) also satisfies specific conditions (i) to (vii):
(i) a density of 0.92 to 0.96 g/cm3,
(ii) a melt flow rate (MFR) of 0.01 to 200 g/10 minutes,
(iii) a molecular weight distribution (Mw/Mn) of 1.5 to 3.5,
(iv) possessing only one peak in terms of the number of peaks observed in an elution temperature-eluted amount curve as measured by the continuous temperature raising elution fractionation (TREF) method, and from the integrated elution curve obtained by said elution temperature-eluted amount curve, the difference T75xe2x88x92T25 in the temperature and said density d respectively follow the relationships shown by formula a and formula b, wherein T25 is the temperature where 25% of the total elution is obtained, and T75, is the temperature where 75% of the total elution is obtained;
(v) possessing one or two melting point peaks, and among these the highest melting point Tm1 and said density d follow the relationship described by formula c;
(vi) an electrical activation energy of no greater than 0.4 eV; and
(vii) the melt tension (MT) and melt flow rate (MFR) follow the relationship shown by formula d.
if d less than 0.950 g/cm3, thenxe2x80x83xe2x80x83(Formula a)
T75xe2x88x92T25xe2x89xa7xe2x88x92300xc3x97d+285
if dxe2x89xa70.950 g/cm3, then
T75xe2x88x92T25xe2x89xa70
T75xe2x88x92T25xe2x89xa7xe2x88x92670xc3x97d+644xe2x80x83xe2x80x83(Formula b)
Tm1xe2x89xa7150xc3x97dxe2x88x9217xe2x80x83xe2x80x83(Formula c)
log MTxe2x89xa6xe2x88x920.572xc3x97log MFR+0.3xe2x80x83xe2x80x83(Formula d)
The resin material for an electrical insulating material comprising this ethylene xcex1-olefin copolymer (A) displays a superior processability and thermal resistance, in addition to superior electrical insulating properties, such as volume resistivity, space charge characteristics, dielectric breakdown strength, water-treeing resistance, and the like, in which a reduction in the mechanical strength does not occur. In addition, the resin material for an electrical insulating material is rich in cross-linkability, and even after cross-linking, exhibits superior volume resistivity, space charge characteristics, dielectric breakdown voltage, water-treeing resistance and the like.
In addition, said ethylene xcex1-olefin copolymer (A) is preferably obtained by means of copolymerizing ethylene and C4-12 xcex1-olefin under the presence of a catalyst comprising a cyclic organic compound containing at least a conjugated double bond, and a compound containing transition metal from group IV of the Periodic Table. The resin material for an electrical insulating material comprising this ethylene xcex1-olefin copolymer (A) displays a more superior processability, thermal resistance, mechanical strength, and electrical insulating properties.
In addition, the halogen concentration within said ethylene xcex1-olefin copolymer (A) is preferably no greater than 10 ppm. The resin material for an electrical insulating material comprising this ethylene xcex1-olefin copolymer (A) does not require the addition of additives such as halogen acceptor or the like, and thus maintains superior electrical insulating properties.
In addition, said resin component may also comprise said ethylene xcex1-olefin copolymer (A), and another polyolefin (Axe2x80x2).
In addition, said other polyolefin (Axe2x80x2) is preferably at least one compound selected from among a polyethylene obtained by means of a high pressure radical polymerization, a high density polyethylene, a medium density polyethylene, and a linear low density polyethylene. The resin material for an electrical insulating comprising this other polyolefin (Axe2x80x2) exhibits superior extrusion molding characteristics.
In addition, said carbonyl or carbonyl derivative group-containing monomer (M1) to be introduced into said resin component is preferably at least one compound selected from among maleic anhydride and (meth)acrylic acid. The resin material for an electrical insulating material introducing this monomer unit results in a large improvement in the volume resistivity.
In addition, a maleic anhydride-modified ethylene xcex1-olefin copolymer (A) is preferably used at the time said carbonyl or carbonyl derivative group-containing monomer (M1) is introduced into said resin component. The resin material for an electrical insulating material comprising this copolymer results in a particularly large improvement in the volume resistivity.
In addition, a polystyrene, an ethylene-styrene random copolymer, or an ethylene copolymer (A), which has been modified by means of grafting an aromatic ring-containing monomer, is preferably used at the time said aromatic ring-containing monomer (M5) is introduced into said resin component. The resin material for an electrical insulating material comprising this copolymer results in a large improvement in the dielectric breakdown strength.
In addition, at least one compound selected from among an liquid polybutadiene, a maleic anhydride-modified liquid polybutadiene, an ethylene-aryl(meth)acrylate copolymer, and an ethylene-vinyl(meth)acrylate copolymer is preferably used at the time said compound or monomer containing two or more ethylenic linkages (M6) is introduced into said resin component. The resin material for an electrical insulating material comprising these polymer or copolymer displays superior electrical insulating properties after cross-linking and an excellent cross-linking efficiency.
In addition, said resin component preferably contains said compound or monomer containing two or more ethylenic linkages (M6) and said carbonyl or carbonyl derivative group-containing monomer (M1). The resin material for an electrical insulating material introducing these monomers shows a superior cross-linking efficiency and volume resistivity.
In addition, a maleic anhydride-modified liquid polybutadiene and a maleic anhydride-modified ethylene cc-olefin copolymer (A) are preferably used at the time said carbonyl or carbonyl derivative group-containing monomer (M1) and said compound or monomer containing two or more ethylenic linkages (M6) are introduced into said resin component. The resin material for an electrical insulating material comprising these copolymers results in large improvements of the electrical insulating properties after cross-linking, cross-linking efficiency, and volume resistivity.
In addition, said resin component preferably contains said compound or monomer containing two or more ethylenic linkages (M6) and said aromatic ring-containing monomer (M5). The resin material for an electrical insulating material introducing these monomers displays a superior cross-linking efficiency, volume resistivity, and dielectric breakdown strength.
In addition, a maleic anhydride-modified liquid polybutadiene and an ethylene-styrene random copolymer are preferably used at the time said compound or monomer containing two or more ethylenic linkages (M6) and said aromatic ring-containing monomer (M5) are introduced into said resin component. The resin material for an electrical insulating comprising these copolymers results in large improvements of the electrical insulating properties after cross-linking, cross-linking efficiency, volume resistivity, and dielectric breakdown strength.
In addition, said resin component preferably contains said carbonyl or carbonyl derivative group-containing monomer (M1) and said aromatic ring-containing monomer (M5). The resin material for an electrical insulating material introducing these monomers displays a superior volume resistivity and dielectric breakdown strength.
In addition, a maleic anhydride-modified ethylene xcex1-olefin copolymer (A) and an ethylene-styrene random copolymer are preferably used at the time said carbonyl or carbonyl derivative group-containing monomer (M1) and said aromatic ring-containing monomer (M5) are introduced into said resin component. The resin material for an electrical insulating material comprising these copolymers results in large improvements of the volume resistivity, and dielectric breakdown strength.
In addition, said resin component preferably contains said carbonyl or carbonyl derivative group-containing monomer (M1), said compound or monomer containing two or more ethylenic linkages (M6), and said aromatic ring-containing monomer (M5). The resin material for an electrical insulating material introducing these monomers displays a superior cross-linking efficiency, volume resistivity, and dielectric breakdown strength.
In addition, a maleic anhydride-modified liquid polybutadiene, a maleic anhydride-modified ethylene xcex1-olefin copolymer (A) and an ethylene-styrene random copolymer are preferably used at the time said carbonyl or carbonyl derivative group-containing monomer (M1), said compound or monomer containing two or more ethylenic linkages (M6), and said aromatic ring-containing monomer (M5) are introduced into said resin component. The resin material for an electrical insulating material comprising these copolymers results in large improvements of the electrical insulating properties after cross-linking, cross-linking efficiency, volume resistivity, and dielectric breakdown strength.
In addition, the electrical insulating material according to the present invention is characterized in using the aforementioned resin material for an electrical insulating material. This electrical insulating material displays a superior processability, mechanical strength, and electrical insulating properties.
In addition, the electrical insulating material according to the present invention preferably comprises a maleic anhydride-modified ethylene xcex1-olefin copolymer (A).
In addition, the electrical insulating material according to the present invention preferably comprises a maleic anhydride-modified ethylene xcex1-olefin copolymer (A) and an ethylene-styrene random copolymer.
In addition, the electrical insulating material according to the present invention is characterized in that a resin material for an electrical insulating described in the aforementioned is cross-linked. This electrical insulating material displays an even more superior mechanical strength.
In addition, the electrical insulating material according to the present invention preferably comprises a cross-linked resin material for an electrical insulating material comprising a maleic anhydride-modified liquid polybutadiene, and a maleic anhydride-modified ethylene xcex1-olefin copolymer (A).
In addition, the electrical insulating material according to the present invention preferably comprises a cross-linked resin material for an electrical insulating material comprising a maleic anhydride-modified liquid polybutadiene, and an ethylene-styrene random copolymer.
In addition, the electrical insulating material according to the present invention preferably comprises a cross-linked resin material for an electrical insulating material comprising a maleic anhydride-modified liquid polybutadiene, maleic anhydride-modified ethylene xcex1-olefin copolymer (A) and an ethylene-styrene random copolymer.
In addition, the electric wire and cable according to the present invention is characterized in using cross-linked or non-cross-linked electrical insulating material described above as an insulating layer. This electric wire and cable display a superior mechanical strength and electrical insulating properties.